DNA vaccines encoding influenza hemagglutinin (HA) antigens offer an important advantage toward influenza pandemic and biodefense readiness in terms of the speed with which new influenza DNA vaccine vectors can be formulated and manufactured following identification of a new threat virus. Importantly, large scale manufacturing of influenza DNA vaccines specific for highly pathogenic viruses can be accomplished in the absence of biological containment requirements. The use of particle-mediated epidermal delivery (PMED) technology offers further advantages in the low DNA dosage requirement, the ability to deliver such vaccines with a reusable, mass vaccination device, and the proven ability of PMED-based DNA vaccines to induce protective level humoral and cellular responses in humans. In this application, we intend to conduct three clinical research trials to establish proof-of-concept for the protective efficacy of PMED influenza DNA vaccines encoding HA. These trials will evaluate the ability of a trivalent PMED DNA vaccine formulation to induce HA-specific humoral and cellular responses to three separate antigens. Evidence for the protective efficacy of these responses will be demonstrated in a human challenge trial. In addition, evaluation of the potential of this approach for pandemic protection will be accomplished by examining the ability of this technology to elicit significant humoral and cellular responses to an H9 pandemic threat virus. Finally, we will focus PMED device development efforts toward a proof-of-concept prototype reusable device that will serve as the basis for a future mass vaccination PMED device. This reusable device will discharge a measured dose of pressurized helium through disposable unit-dose nozzles. These nozzles will be designed to facilitate manufacturing scale-up and to deliver increased DNA/gold payloads to larger skin target areas as a means of increasing the effective vaccine dose.